This invention relates to elastomeric polyisocyanate-based polymers, particularly polyurethane and/or polyurea polymers prepared from polyoxyalkylene polyols containing internal polyoxyethylene blocks.
It is well-known to prepare polyurethane polymers by reacting an organic polyisocyanate with an isocyanate-reactive composition comprising a polyether polyol or a polyester polyol. Advantageously, when preparing elastomeric polyurethanes it is also known to incorporate a chain-extending agent into the isocyanate-reactive composition.
When preparing elastomeric polyurethanes from polyester polyols, the resulting polymers have good physical properties, but may only be prepared under difficult, undesirable process conditions. Polyester polyols are frequently highly viscous liquids or low melting point solids at room temperature. It is therefore necessary to conduct such processes employing polyester polyols at an elevated temperature or employ specialized equipment capable of handling high viscosity components.
An alternative to using polyester polyols is to use polyether polyols in the preparation of elastomeric polyurethane polymers U.S. Pat. No. 4,440,705 discloses the use of polyether polyols in the preparation of polyurethane elastomers. The polyether polyols described are polyoxypropylene polyols end-capped with polyoxyethylene blocks. The polyoxyethylene blocks are present in such concentrations to provide sufficient primary hydroxyl content allowing for high reactivity and short mold cycle times.
However, to obtain elastomeric products which have similar properties to those prepared from polyester polyols, especially with respect to resistance to abrasive wear, it has been necessary to employ polyether polyols exhibiting strong cohesive interactions such as, for example, polytetramethylene glycol.
Alternatively, it is possible to enhance the cohesive interactions by extending the polyoxyethylene end-cap of the polyol. However, in this case undesirable polar interactions may be encouraged leading to turbidity of the polyether polyol. The presence of turbidity is disadvantageous as it can cause processing difficulties in preparing the elastomer and provide an elastomer with inferior physical properties. Such polyether polyols, as polyester polyols, can require high processing temperatures as turbidity frequently is associated with higher viscosities.
In Canadian Patent 1,133,650 it is taught to prepare copolymer polyols from ethylene oxide and propylene oxide where the ethylene oxide is distributed internally within the oxyalkylene chain and as a terminal oxyethylene cap. The internal ethylene oxide is taught as providing for solubility of the chain-extending agent and the terminal oxyethylene cap provides for required processibility characteristics and physical properties of the resulting elastomeric polymer.
In the published patent specification, GB 1,063,278 it is taught to prepare elastomeric polyurethanes from polyether polyols having a hydroxyl equivalent weight of from 3400 to 8000 and containing butylene oxide and from 10 to 50 weight percent ethylene oxide distributed randomly. The resulting elastomers are disclosed as having enhanced abrasion resistance, low hardness and low temperature properties compared to elastomers prepared from lower equivalent weight polyether polyols.
However, the incorporating of ethylene oxide into a polyether polyol for use in elastomeric polymer preparation has some disadvantages. The ethylene oxide content provides a more polar polyol which has a greater hygroscopic tendency and therefore the corresponding elastomeric polymers display similar characteristics. Such polymers are susceptible to hydrolysis and are therefore unsuitable for applications where prolonged exposure to humid conditions may occur.
It is therefore desirable to prepare an elastomeric polyurethane polymer from a polyether polyol that provides for optimum abrasion resistance properties and yet which is a clear, low viscosity liquid allowing for good processability at, for example, room temperature. It is further desirable that such a polyether polyol provides for similar or improved physical properties as for existing polymers.